1. Field of the Invention
This invention generally relates to a system for, and a method of, holding optical accessories, e.g. filters, polarizers and the like, in front of a lens such as a camera lens.
2. Description of Related Art
It is known to mount matte boxes, filter holder assemblies and analogous accessory holders in front of a camera lens to achieve a desired cinematographic effect. Reference can be had, for example, to the following U.S. Pat. Nos.: 4,381,885; 4,443,061; 4,563,063; 4,901,098; 4,487,312 and 4,063,266.
As described in at least some of these patents, the accessory holder is provided with a channel in front of the camera lens, and the accessory, usually a filter, is inserted into the channel. A "bare" filter itself may be grasped at its outer edges and positioned directly in the channel. However, to avoid direct grasping and touching of the bare filter itself, the filter is often placed within a frame, and the "framed" filter may be grasped, typically by a protruding handle, and positioned directly in the channel.
Although generally satisfactory for their intended purpose, the known accessory holders have not proven to be altogether desirable in practice. It is inconvenient and difficult to precisely position a bare or framed filter in a desired position within the channel. The push/pull force required to overcome friction between the filter and the channel is not uniform, nor easily controlled with any high degree of precision.
It is further known to mount a filter in a frame that has a rack along one edge. A mating pinion gear is then rotated to re-position the filter. However, the requirement for a racked frame and pinion gear adds to the overall weight, bulk and manufacturing cost.
Another problem with known accessory holders is that the filters may accidentally fall out of the channel, especially when the holders are rotated about 180.degree.. Typically, set screws are used to lock the accessory in place within the channel. However, the leading edges of the set screws mar the accessories themselves. Also, failure to adjust the set screws can result in the accessory falling from the holder. When the accessory is a glass filter, it is prone to breakage upon striking the ground.
Still another problem with known accessory holders is the lack of a convenient means for rotating a holder to a desired angular orientation, and then locking the holder in that orientation. It is known to advance a set screw mounted in a rotary holder for the purpose of locking the holder in place. However, the known construction is disadvantageous, principally because the set screw tends to scratch and unduly wear the surface against which it bears. Also, the set screw requires many turns to advance it to a locking position and does not provide the user with an adequate tactile or visual indication of its locking position.